1. Field of the Invention
The invention concerns a probe for taking samples of an analyte located in the fluid medium, the probe including a membrane which closes the probe to the outside, the membrane being permeable to the analyte, a flow-through cell positioned behind the membrane, and at least one incoming and outgoing line leading to or from the flow-through cell.
2. Description of The Related Art
In chemical analysis it is frequently desired that particular components of a system are detected or monitored and that this occurs via a measurement probe. To this end various probes are in use, each designed depending upon the particularities of the various analytical possibilities. For example, probes are known which contain electrodes or polarographic sensors and which are closed off towards the outsidexe2x80x94that is, with respect to the medium being analyzedxe2x80x94by a membrane. Such probes contain, among other things, a stationary fluid, such as an electrolyte or a buffer solution. Further, it is known to have probes for measurement using a flow-through process, that is, that the substance to be analyzed (the analyte), after passing through the membrane and entring into the probe, is transported to a remote measuring system for taking measurements.
In DE-AS 26 50 730 B1 and WO 97/08533 A2 a submerged dialyzer is described, in which a membrane is applied directly upon a replaceable probe part, which includes an incoming and outgoing line. The membrane is so tensioned over the head of the probe part, that it is removable. In order to guarantee an even distribution of the buffer under the membrane, ruffles or ridges are provided in the head of the probe part. Since the membrane is frequently very thin and sensitive, changing out of the membrane, and cupping of the membrane over the head, is quite difficult. Besides, the exchange surface between the fluid medium situated outside of the membrane and the medium flowing through the ridges is relatively large and unspecified.
In DE-OS 2 310 264 a similar probe is described, in which the incoming and outgoing lines are wound in the form of a helix.
In EP 0 054 537 A1 a probe carrier is described, in which the membrane is applied directly upon the probe carrier. The arrangement is so provided on a housing, that the membrane cannot be replaced in a simple manner. Besides this, the exchange surface over the flow-through cell cannot be varied.
In DE 297 01 652 U1 a probe is described, in which a membrane is laid upon the probe part and is secured from the outside using a membrane holder. The membrane holder has a defined opening, so that a fluid medium can pass through the opening to the membrane and from this to a flow-through cell. The exchange surface between the membrane and the flow-through cell is determined by a through-hole, which is situated behind the membrane in the probe part. Since the membrane is clamped between the probe part and the membrane holder, the replacement of the membrane is difficult. Besides this, the exchange surface area is permanently predetermined by the probe and cannot be varied.
A similar probe is described in DE-OS 31 26 648 A1, in which the membrane is introduced in the opening of a membrane holder which can be screwed upon the probe. Thereby the problem occurs, that the membrane surface towards outside is predetermined by the through-hole in the membrane holder, which at the same time determines the exchange surface.
In WO 96/07885 A1 a probe with a circular shaped surface is described, in which a membrane is glued directly upon a membrane holder, and wherein a communication channel for an incoming and an outgoing line is provided between the membrane and the membrane holder. The probe has the disadvantage, that the membrane is not easy to replace and is adhered. It cannot be employed in extreme environmental conditions, since an adhesive bond in this form cannot be made sterile-tight and would dissolve or release during steam sterilization. Further, the membrane is completely open upwards and offers a maximal exchange surface.
The herein described probe type is suitable for taking samples from a fluid medium, wherein the analyte comes into contact with an acceptor (medium) after entry into the probe, which via an incoming and outgoing line is channeled to a flow-through cell proved in the probe.
It is thus the task of the invention, to provide a probe, in which the membrane and the membrane holder are easy to replace and with which a defined exchange surface with the flow-through cell can easily be varied, while using an otherwise identical or standard membrane. The probe should herein be capable of being employed in extreme analyte conditions, that is, should be sterilizable by steam and should be sterile-tight.
The probe is to be so designed or equipped, that even minute amounts of analyte can be removed, and that sample volumes can be kept small, insofar as this is desired.
For solving this task provision is made to introduce the membrane between two membrane seals and with these to form a unit, wherein the membrane seals respectively have a passage or through-hole to the membrane holder or as the case may be the probe part, and the unit is provided between the membrane holder and the probe part and is securable to the probe part via the membrane holder in a replaceable yet sealing manner. The membrane holder is in the form of a gland and provides, by means of the through-holes of the membrane seals, for only a defined limited surface of the membrane to be exposed over the flow-through cell.
It is thus proposed, that the membrane holder defines the exchange surface over the flow-through cell. The membrane holder is thereby positioned before the membrane and the probe part and sealingly and releaseably clamps the membrane tightly to the probe part. The membrane is provided between two membrane seals and forms thereby a sandwich structure type unit, which is easily exchangeable and easy to manipulate and besides this has a good sealing effect. Thereby the membrane and membrane holder are removable as a single unit, so that the exchange surface can be changed by a simple unscrewing of the unit comprised of membrane and membrane holder and replaced by another unit dimensioned as needed.
An elementary difference in comparison to the conventional probes is comprised therein, that the membrane is provided tightly or fixedly between the membrane seals, so that the normally thin and sensitive membrane can be exchanged together with the membrane seals, wherein this unit and the membrane holders are premade.
The inventive probe is preferably a pure sample-taking probe; the actual measurement is undertaken in conventional manner outside of the probe, but it can however also occur within the flow-through cell. In the later case the flow-through cell must be supplementally provided with at least one sensor as well as circuits or conductors going to the sensor for control of the measurement process and for relaying or communicating the measurement results. These measures as such are known and are thus not described in greater detail herein.
The measurement can occur via various measurement processes. If the measurement is carried out outside of the probe, then there is through the conduits an acceptor flow directed to the flow-through cell which is closed off to the outside via the membrane and subsequently flows out of the probe through the outgoing lines and is supplied to the measurement unit. The acceptor flow can be directed continuously through the probe. It is possible, to interrupt the acceptor flow, so that a defined enrichment of the analyte defusing through the membrane can occur in the acceptor. The control of the acceptor flow occurs however likewise from outside the probe and is thus not discussed in greater detail herein.
An important characteristic of the invention is comprised therein, that the membrane is connected to an isolated membrane holder.
The production or premanufacture of a unit comprised of membrane and membrane holder offers many advantages. First, the unit comprised of membrane and membrane holder makes possible a simple exchange of the membrane with another membrane connected with an appropriate membrane holder. In this manner, used membranes can be easily changed and respectively different membranes can be used selectively for various measurement process and/or analytes using the same probe. Since the membrane is connected with the holder, the exchange of the frequently thin and sensitive membrane is easy to accomplish. The membrane can for example of adhered to the holder, or it can be secured to the holder via suitable securing means.
A further important feature of the invention is comprised therein, that the membrane holder forms a gland and only a defined surface of the membrane (over the flow-through cell) is exposed as an exchange surface, through which the analyte can penetrate into the flow-through cell from outside. For the measurement and evaluation of the analyte it is important, that the exchange surface between the fluid medium originally containing the analyte and the acceptor situated in the flow-through cell is precisely determinable, and that one can in certain cases exercise influence over this exchange surface.
The membrane holder is thus so designed, that a defined surface area of the membrane situated over the flow-through cell and connected therewith is exposed, through which the analyte can penetrate. It is thus possible to have available various units of membrane and membrane holde for conducting various measurements in which the membrane holder exposes respectively various surface areas with an otherwise identical membrane.
In a further development of the invention it is envisioned, that the flow-through cell within the probe has an elongate form along the membrane. The elongate form is a particularly suitable geometry for a flow-through measurement, since a discontinuous or interrupted flow process, with uniform-as-possible acceptor dwell times, can be achieved. Besides this it is useful, to maintain the acceptor below the membrane to a thin layer thickness.
The flow-through cell canxe2x80x94in one embodiment of the inventionxe2x80x94be formed or designed having one channel introduced in the membrane and one in the seal which may in certain cases be associated therewith. Thereby it is optimally achieved, that the acceptor medium during the course of the exchange or, as the case may be, the entry of analyte, occurs in a thin layer directly along the membrane.
The incoming and outgoing lines can advantageously be provided on the back side of the elongated flow-through cell.
In an advantageous embodiment of the invention the incoming and outgoing lines are comprised of capillaries, between which the (preferably elongate, channel-like) flow-through cell is provided.
It is further advantageous, that the probe as a whole is shaped like a tube, wherein the flow-through cell and the unit comprised of membrane and membrane holder are provided on one end of the tube and wherein the incoming and outgoing lines lead to connections on the other end of the tube. Depending upon the selected length of this tube, the sample collectionxe2x80x94which occurs at the lower end of the tube by passage of analyte into the flow-through cellxe2x80x94can be positioned or located at the desired point within the system to be examined. The probe can thus be designed to be both compact as well as long. The differences herein would essentially only be in the length of the incoming and outgoing channels and the length of the probe body.
A unit comprised of membrane and membrane holder can, for example, be screwed onto the probe. However, other coupling possibilities are possible.